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Doctoral Degrees (Plant Breeding)

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Browsing Doctoral Degrees (Plant Breeding) by Author "Abraha, Mizani Tesfay."

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    Breeding tef [Eragrostis tef (Zucc.) trotter] for drought tolerance in Northern Ethiopia.
    (2016) Abraha, Mizani Tesfay.; Shimelis, Hussein Ali.; Liang, Mark.
    Tef is the leading crop in Ethiopia for human food and animal feed. Worldwide tef is becoming a popular health food due to its gluten-free property. Productivity of tef is low in Ethiopia, with a mean of 1.6 t haˉ¹, which is well below potentially attainable yields of over 4 t haˉ¹. In the past the national tef improvement program has developed improved tef varieties. However, adoption of these varieties in the moisture-stressed tef growing areas has been limited because of their late maturity and the frequent occurrence of terminal drought. Development of tef varieties with high yield potential and adaptation to moisture stress is the overriding consideration in Ethiopia. Therefore, the overall goal of the study was to contribute to food security in Ethiopia, through improving the yield and productivity of tef. To achieve this, a research project was conducted aiming to develop drought tolerant tef varieties with farmer preferred traits, wide adaptation and better performance under moisture stress. The specific objectives of the study were: (1) to asses tef production constraints, management practices, input use, farmers’ trait preferences and breeding priorities in northern Ethiopia, Tigray Region; (2) to determine the genetic diversity of tef genotypes for drought tolerance using phenotypic and molecular markers, and to identify promising tef genotypes for improving moisture stress tolerance and grain yield; (3) to estimate the level of genetic variation, inheritance and trait association of tef genotypes; and (4) to determine gene action and inheritance of drought tolerance in tef and to identify better performing populations in moisture-stressed and non-stressed environments, and to advance these through the single seed descent method. Different research activities were conducted that contributed to these objectives. Participatory rural appraisal research was conducted in northern Ethiopia in four selected districts of three administrative Zones of the Tigray Region, namely, Laelay-Maichew, Medebay-Zana, Ahferom and Alamata. Primary data was collected from a total of 240 sampled farmers and secondary data was collected from the Bureau of Agriculture and Rural Development (BoARD). Data was coded and analysed using SPSS software. Results indicated that improved varieties were used by the majority of respondents in all districts and fertilizers in all except Alamata, where severe moisture stress dictated the choice of variety and reduced fertilizer application. High grain yield, increased panicle length and straw yield were the most important farmer-preferred traits. In Alamata District, early maturity was the third preferred trait while straw yield ranked fourth. Transplanting maximized the yield of tef, but a cost-benefit analysis showed that direct row sowing was more profitable. Moisture stress (reported by 60.4% respondents, weeds (61.2%), shoot fly (58.2%), lodging (53.3%) and seed shattering (60.8%) were rated as severe tef production constraints in the study areas. Farmers estimated that moisture stress caused yield losses of 37%, 49%, 48% and 60%, in the Laelay-Maichew, Medebay-Zana, Ahferom and Alamata districts, respectively. This study prioritized production constraints and farmers’-preferred traits useful in the breeding of tef to enhance its productivity in drought-prone environments in northern Ethiopia. One hundred forty four tef genotypes were evaluated using four experiments representing optimum moisture and moisture-stressed environment in the 2014 main and off seasons. Genotypes, DZ-Cr-387, DZ-01-787, DZ-01-3186, 9432, 9403, 9415, 205917, 205896, 215678, 213237, Jano, Kaye-Agachew, Purpurea, Kaye-Murri and Dschanger were selected as promising parents with superior grain yields, reduced lodging, tall plant height and long panicles in a non-stressed environment. Conversely, genotypes, DZ-Cr-385, DZ-Cr-37, HO-Cr-136, DZ-01-2053, Dabbi, 207832, Zagure and Shawa-Gemerra were selected as superior parents for their early maturity and high yield performances under moisture-stressed conditions. Main shoot panicle seed weight had high genotypic coefficients of variation (GCV) of 22.4% and 25.9% under non-stressed and stressed conditions, respectively. Grain yield had GCV values of 17.6% and 20.0% in the corresponding environments. Heritability was higher under optimum conditions than moisture stressed conditions. Days-to-maturity, plant height, panicle length and panicle seed weight were positively correlated with grain yields under non-stressed conditions, while these traits negatively correlated with grain yield under moisture stressed conditions. A path-coefficient analysis indicated that direct selection for high biomass, harvest index and late maturity could increase grain yield under optimal condition, while under moisture stressed conditions early maturity, high biomass and harvest index were important direct selection criteria for tef breeding aiming for drought tolerance. The genetic diversity of 60 selected tef genotypes was determined using 10 selected diagnostic and polymorphic simple sequence repeat (SSR) DNA markers. The number of alleles per locus varied from 10 to 23 with a mean of 16. The polymorphic information content (PIC) ranged from 0.64 for marker CNLTS11 to 0.94 (CNLTS136A/B) with a mean of 0.84, suggesting sufficient discrimination power of the markers for the tested genotypes. The analysis of molecular variance showed that 63% and 35% of the total variability could be attributed to differences within and among tef genotypes, respectively. Overall, the SSR analysis identified distinct genotypes such as DZ-Cr-385, 222076 and 213237, which are known for their early maturity and good yields under moisture stress. The analysis also identified genotypes DZ-Cr-387, 205896, 205917 and Dschanger, which was consistent with their unique agronomic attributes such as late maturity, high grain yields, relatively good plant heights and long panicles under optimum rainfall conditions. The identified agronomic complementary tef genotypes are valuable genetic resources for further breeding. Seventeen crosses along with their eight parents were evaluated in the F2 generation under moisture-stressed and non-stressed conditions in northern Ethiopia during 2015 and 2016. Additive gene action predominantly controlled the inheritance of grain yield, biomass yield, harvest index, days-to-panicle emergence, days-to-maturity, panicle length, plant height, main shoot panicle seed weight, number of productive tillers per plant and relative water content under both the moisture-stressed and non-stressed conditions. Non-significant general combining ability (GCA) and specific combining ability (SCA) effects were detected for biomass yield, relative water content and peduncle length under non-stressed conditions. Under both test conditions genotypes, DZ-Cr-387 and 9415 were the best general combiners for increased grain yield and yield components, except for days-to-maturity. Conversely, genotype 222076 was the best general combiner for reduced maturity period only. The families of DZ-Cr-387 x 207832 and DZ-Cr-387 x 222076 were high grain yielders with early maturity under both test conditions. There were marked genotypic and phenotypic variations, among the crosses in the F2 generation, allowing for successful selection and genetic advancement. Overall, the study identified valuable tef genotypes with high combining ability for yield and yield components in drought-stressed and non-stressed environments. It also initiated the development of novel tef families that will be further evaluated for cultivar development and release.